Niobium based paints and coatings, its oxides and anticorrosive use

ABSTRACT

The present invention refers to compositions and coatings, having the niobium, its oxides and possible associations with other oxides as a pigment, and its utilization carried out by the usual techniques of painting, acting as an anticorrosive to organic acids, particularly the naphthenic acids in sulfide medium, persistently present in the petrochemical industry.

TECHNICAL FIELD

[0001] The innovation refers to paints and coatings based on Niobium,its oxides and possible associations with other oxides, and its use madeby the usual painting technique and not by the electro depositiontechnique by founded salts or equivalents, used in galvanoplasty. Theinvention purpose is to neutralize the high corrosive effects ofnaphthenic acids and sulfur compounds which rapidly destroy the carbonsteel and special alloys such as the stainless steel of, practically,all the chromium and nickel alloy families.

FORMER TECHNIQUES

[0002] The corrosion by naphthenic acids has been, for years, a seriousproblem in the oil refining industry. The first case was observed in1920 and for 35 years, it lingered on without any specific studies. W.A. Derungs reported one of the first works, presenting problems occurredin refineries caused by the attack of naphthenic acids and sulfurcompounds. The literature makes reference to the naphthenic corrosion inthe refining of some crude originated in India, Russia and Venezuela. InBrazil, the problem has been detected during the processing of thenational oil, reaching high corrosion rates close to 7 mm/year.

[0003] The literature also mentions that this type of corrosion occurswhen the petroleum presents total acid number (TAN) equal or higher than0.5 mg KOH/g crude in temperatures varying from 220 to 440° C. and inhigh draining speeds. These speeds reach from 60 to 100 m/s in therefining process. An additional problem is that the corrosion caused bythe brimstone(sulfur) compounds could also occur under the sameconditions as the naphthenic corrosion.

[0004] Many materials have been tested on the field and presented poorperformance under most operating conditions. Due to these results, weintroduced the niobium in the oxide form as an alternative coating thatcould be used in the combat to naphthenic corrosion.

[0005] There is very little reference about the niobium utilization as aprotector agent against the corrosion; however, it is known to exist arequest for a French patent, originated from the doctorate thesis of A.TRAVALLONI—“Depot Eletrolytique de Niobium a partir de FluoruresFondus”—Pierre et Marie Curie University—Paris (1978), based on theelectro deposition by founded salts with pyrochlore base. Likewise, itis well documented in the technical literature the niobium utilizationas an anticorrosive element, but also as a favorable element to resistto cold fragility.

[0006] Following, we will present the experimental evidences thatconfirm the niobium resistance in the petroleum presence.

[0007] To simulate the operational conditions of a refinery, some essayswere carried out according to the ASTM G1.05.04 norm, that basicallyconsisted of the immersion of the material pieces to be studied. In ourcase, we studied carbon steel, AISI 410 steel, 9%-Cr steel and themetallic niobium. We used an oil as a corrosive medium with TAN biggerthan 0.5 mg KOH/g and total sulfur of 0.5% m/m.

[0008]FIG. 1 illustrates, in graphic form, the behavior of the essayedmaterials in autoclave, with the vertical axle representing thecorrosion rate (mm/year) and the horizontal one representing the initialpressure (psi).

[0009] With the aide of X-ray diffraction and of the Auger'sspectroscopy, it was possible to verify the main constituents of thefilms. The evidence was that a sulfide film (Pyrrhotite or Troilite) wasformed on steel while a film of niobium oxide was formed on the niobium(Nb_(x) e O_(y)). FIG. 2—carbon steel surface, FIG. 3—carbon steel after3s, FIG. 4—niobium surface and FIG. 5—niobium after 30s present theresults of the Auger's spectroscopy, but in all figures the verticalaxle represents the intensity and the horizontal axle represents thekinetic energy (eV).

[0010] Under the oil production conditions, the presence of naphthenicacids as corrosive agents is observed since their pre-heating, around200 to 250° C., up to the distillation operations, that are carried outat the refineries with temperatures around 300 to 350° C. and pressuresat the atmospheric pressure level. Under these conditions, the waterpresence is unlike to occur—measured by the so-called “B.S.W.index”—taking us to use a thermodynamic theory in high temperatures,where the water fugacity (H₂O_(v)) is not taken into account.

[0011] The analysis made on the corrosion products revealed the FeSpresence, more precisely of Pyrrhotite (Fe₇S₈) and of Troilite (FeS), inthe scope of our experiments, by the X-ray diffraction as well as byAuger's spectroscopy. As above mentioned, in that niobium case, theessays disclosed that there is always niobium oxide formation and, intest conditions, the H₂S attack is not taken into account.

[0012] The results suggest that the niobium oxide (Nb_(x)O_(y)) presentshigh probability of a protecting performance, once that the formed filmis adherent, is not voluminous and is chemically inert in the corrosivemedium.

[0013]FIG. 6 represents the thermochemical diagram for the Nb-O systemand shows that the stable oxides, sensitive to react to the niobium inhigh temperatures and pressures, are: NbO, NbO₂, Nb₂O₅, in increasingorder of oxidation. We also observed, at the temperature of 330° C. usedin our essay, the potential values (E_(soe)) of −1.8V in relation to theoxygen and gas electrode.

[0014] The presence of Nb_(x)O_(y), demonstrated by the Auger'sspectroscopy analysis, came to ratify the results presented in FIG. 1 asbeing an extremely protecting oxide in naphthenic medium +H₂S.

[0015] In effect, we observe in this figure that the corrosion rate ofoxidized niobium—NbO—is around 0.001 mm/year, in contrast to carbonsteel that, for the initial pressure of 70 psi is around 0.008 mm/year,as well as for the AISI 410 steel (0.600 mm/year) and for the 9%-Crsteel (0.500 mm/year). Even under essay conditions, the lightest (20psi), the good performance of the niobium is evident.

[0016] As for the iron behavior in experimental tests, we observed anextremely high corrosion of this material with the presence of FeS andFe₇S₈ as corrosion products. The thermodynamic explanation for thepresence of these products could be easily deduced in the Fe—S—Odiagram, chemically inert in this corrosive medium. These resultsintroduce the metallic niobium and their oxides, as materials withpotential to be explored for the use as a coating at the oil refiningunits.

INVENTION SUMMARY

[0017] In its most general aspect, the present invention proposecompositions which include pigments, resins, charges, solvents andothers components, comprising a painting method able to be applied oncarbon steel surfaces and other metallic materials of common use in thepetrochemical industry.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention specifically refers to formulationsconsisting of a choice of resins and compatible pigments amongthemselves, so that the paint complies to normal standards of fluidity,covering power, homogeneity, coloring, electrochemical potentials, CPCand adequate CPVC.

[0019] The basic resin is of the epoxy family for temperatures up to100° C., however, it can be utilized the basic resins of the siliconefamily for temperatures up to 600° C.

[0020] The pigments are of the niobium oxides family, genericallydescribed as Nb_(x)O_(y), with X varying from 1 to 2 and Y from 1 to 5.

[0021] The above mentioned components obey the following features:

[0022] RESINS

[0023] Epoxy: They are obtained by the reaction between epichlorhydrinand bisphenol. The paints produced with this resin have two components,one having the pre-polymer epoxy, and the other one having the cureagent which is, generally, one amine or amide. The drying or cure of theepoxy paint occurs by the polymerizing (condensation) process. For aperfect performance, it requires a complete surface cleaning, beingusual the application over a blasting to the almost white or whitemetal.

[0024] Silicon: Are semi-organic resins where silicium atoms are foundin their molecules. The paints made with these resins are indicated forsurface painting at temperatures higher then 120° C., and could be usedfor equipment painting at temperatures up to 500 or 600° C. The cureshould be made by the equipment warming, generally made at the rate of50° C. per hour. PIGMENT: Fusion point: 1520° C. Density: 4.47 g/cm³ %Nb_(x)O_(y):  99.4 Sulphur ppm:  10 Fe ppm: 229 Pb ppm:  <1Granulometry: −45 to 5.6 μm

[0025] The compatibility between resins and pigments is carried outthrough charges, as for the silicate family.

[0026] The proposed formulations refer to the examples 1 and 2, andconsist in the blend of two components, denominated A and B. Thepreparation of each component is made according to the procedure below.

[0027] To prepare component A, initially we dissolve the resin, if it isdry base, otherwise it could be presented as in FIG. 7 (thermochemicaldiagram to the Fe—O—S system).

[0028] In fact, according to this diagram, for the operationalconditions of our tests and for the same calculated value of E_(soe) (inthe case of Nb—O with −1.5V), the estimated value for the oxygenpressure is 10⁻⁶⁸ atm. We observed on this diagram that regions withpotentials below −0.95V are sulfide stability regions, therefore showingthat in our tested scene we have few probabilities to obtain any ironoxide.

[0029] These results are according with the EARL and SVEN works, whichrepresent the Fe—S—O balance (FIG. 8—thermochemical diagram for theS—Fe—O system), at the temperature of 800K, where the stability regionsof the iron, its oxides and sulfides are shown. On this diagram, weverify that on the sulfides stability field, the oxygen pressures arevery small and the sulfur pressures vary from 1 to 10⁻¹⁵ atm, while theP_(H2)/P_(H2S) is proportion is from 10⁻¹ to 10³ atm.

[0030] As for the sulfide presence, it is important to stress thatpresently, the refineries are processing the oil with high sulfurcontent, and when the conditions are favorable to the sulfidesformation, the equipment suffers severe attacks, what can be translatedin factors such as the steel type, the temperature and the drainingspeed, as mentioned before.

[0031] Finally, the results show that under severe attack conditions onthe steel with the presence of naphthenic acids and the sulfurcompounds, the niobium keeps immune or inactive. The niobium oxide isadherent, protecting and used in a resin already dissolved. To theproposed compounds we used one epoxy resin with 24.1% of weight(example 1) and 19.2% associated with one silicon resin with 4.8% ofweight (example 2). Next anti-sedimentation components and niobium oxidewere added, with a variable percentage ranging from 30 to 40% in weight.Sequentially, a vegetal oil was added (1.32% weight) and finally alittle of solvent to adjust the mixture viscosity. This adjustment canbe made using a cup Ford 4, where the ideal adjustment ranges between 17to 23 seconds (examples 1 and 2).

[0032] The preparation of component B consists in mixing the polyamide(72.2% weight) and amine (5.1% weight) with acetone (22.7% weight). Whenthe two components A and B are made, they are mixed at the proportion of8:1.

[0033] To prepare the paint we could use two procedures described below.

PROCEDURE 1

[0034] Using an ironclad ball mill, add all the components and grind for3 to 5 hours to obtain the paint uniformity.

PROCEDURE 2

[0035] Using a plain ball mill, dissolve the resin with solvent by amoderate mechanic shaking method (500 to 700 rpm). When the resin isthoroughly dissolved, add the other components and continue shakingagain until the mixture reaches a homogeneous state. The mixture is thentaken to the milling to obtain the niobium based paint.

[0036] The final product must be stored in a dry and ventilated place,protected from the solar rays at a room temperature lower then 46° C.(examples 1 and 2).

[0037] In the example 3 we present the formulation of a mono-componentpaint, that basically consists of mixing a silicon resin (50% weight)with the niobium oxide (50% weight).

[0038] The present invention is now illustrated by the examples below.The % notation refers to the weight percentage, based in the totalweight of the combination.

EXAMPLE 1

[0039] Component A Epoxy 24.1% Niobium oxide 36.1% Acetone 36.1% Pearlysilica  2.4% Castor oil  1.3% Component B Polyamide 72.2% Amine  5.1%Acetone 22.7%

EXAMPLE 2

[0040] Component A Epoxy 19.2% Silicone 4.8% Niobium oxide 36.1% Acetone36.1% Pearly silica 2.4% Castor oil 1.3% Component B Polyamide 72.2%Amine 5.1% Acetone 22.7%

EXAMPLE 3

[0041] Silicone 50% Niobium oxide 50%

[0042] To obtain the paint according to the formulations above, it isenough to mix the pigment to the resin, anti-sedimentary components,dispersants and solvents.

[0043] Once the paint is obtained, it can be applied up to 6 hoursaccording to the resins characteristics, thus assuring the paintstability for application. It can be applied using a regular paintbrush, pistol or roll.

[0044] Warnings—Some procedures should be observed during the paintingprocess: a) the surface temperature should be at 3° above the dew pointand at a maximum value 50° C. b) the relative humidity should be near to85%.

[0045] As for the surface preparation, preferably it should be used a SA2,5 or SA 3 jet blast. In the impossibility of blasting a mechanictreatment according to ST3 pattern can be used.

[0046] The present paint should have for each coat, 180μ of humidpellicle obtaining a dry pellicle of 100μ.

[0047] After the application, the paint must present the characteristicsbelow.

[0048] A) Electrode potential: up to 100° C., the electrochemicalpotential measured according to the saturated calomel, must present thevalue of −700 mV_(ecs).

[0049] B) HCl instillation of P.A purity:—it should not presentdeteriorations on the paint coating. If it presents a yellow oxidationit is a normal a characteristic of the oxide reaction.

[0050] The present invention does not limit the compositions presentedin the examples, but we could extend the compositions containing,besides the niobium oxide, others oxides, like aluminum, zinc andchromium oxides, among others.

1.- “NIOBIUM BASED PAINTS AND COATINGS, ITS OXIDES AND ANTICORROSIVEUSES”—being: the basic resin of the epoxy family for temperatures up to100° C. and of the silicone family for temperatures up to 600° C., usingniobium oxides as a pigment, generally described as Nb_(x)O_(y), with xvarying from 1 to 2 and Y varying from 1 to 5 with the followingcharacteristics: a) fusion point at 1520° C.; b) b) density 4.47 g/cm³;Nb_(x)O_(y) is 99.4; sulphur ppm is 10; Fe ppm is 229; Pb ppm is smallerthan 1; c) granulometry from −45 to 5.6 μm; being the compatibilitybetween the resins and the pigments obtained through charges, similar tothose of the silicate family, characterized to obtain, for bi-compoundpaints, compositions obeying the following formulations:—for componentA, resins in the proportion from 9.2 to 24.1% in weight, based on thetotal weight of the composition, niobium oxide in proportion from 30 to40%, acetone in proportion from 20 to 30%, pearly silica in proportionof 2.4% and castor oil in proportion of 1.3%;—for component B, polyamidein proportion from 70 to 80% in relation to the total solids, amine inproportion from 5 to 6% and acetone in proportion from 20 to 30%. 2.-“NIOBIUM BASED PAINTS AND COATINGS, ITS OXIDES AND ANTICORROSIVE USE”,according to claim 1, characterized to present to mono-compounds paints,compositions in accordance with the following formulations: siliconebased resins at the proportion of 50% weight, based on the total weightof the composition and the niobium oxide at the proportion of 50%. 3.-“NIOBIUM BASED PAINTS AND COATINGS, ITS OXIDES AND ANTICORROSIVE USE”,according to claim 1, characterized for the direct use of this paintover common steel and by the classic methods of painting, like:paintbrush, pistol, among others. 4.- “NIOBIUM BASED PAINTS ANDCOATINGS, ITS OXIDES AND ANTICORROSIVE USE”, according to claim 1,characterized that the paint can be applied at room temperature as wellas in high temperatures up to a maximum of 600° C., depending on thecharacteristics of the applied resin. 5.- “NIOBIUM BASED PAINTS ANDCOATINGS, ITS OXIDES AND ANTICORROSIVE USE”, according to claim 1,characterized that the paint application can be carried out at the placeof utilization, not being necessary to remove the pieces or parts toother spaces where the atmosphere is controlled. 6.- “NIOBIUM BASEDPAINTS AND COATINGS, ITS OXIDES AND ANTICORROSIVE USE”, characterized bythe use of niobium and its oxides as pigments, in compositions intendedto inhibit the corrosion of organic acids, particularly the naphthenicacids in sulfide medium. 7.- “NIOBIUM BASED PAINTS AND COATINGS, ITSOXIDES AND ANTICORROSIVE USE”, according to claim 1, according to theclaim 6, characterized by the use of niobium and its oxides as pigmentsin associations with other oxides, like the chromium oxide, zinc oxide,aluminum oxide, among others.